applicant): Mucormycosis is a life-threatening infection that occurs in patients who are immunocompromised due to diabetic ketoacidosis, neutropenia, organ transplantation, and/or increased available serum iron. Because of the rising prevalence of diabetes, cancer, and organ transplantation, the number of patients at risk for this deadly infection is on the rise. Despite aggressive therapy, which includes disfiguring surgical debridement and adjunctive toxic antifungal therapy, the overall mortality of mucormycosis remains >50%, and it approaches 100% in patients with disseminated disease. Clearly new strategies to prevent and treat mucormycosis are urgently needed. Clinical hallmarks of infection by Rhizopus oryzae, the most common cause of mucormycosis, include the unique susceptibility of patients with increased available serum iron, the high propensity of the organism to invade and traverse blood vessels, and defective phagocytic function, which we hypothesize to be, at least in part, a result of iron toxicity. These clinical hallmarks underscore the critical role of iron metabolism, as well as interactions with endothelial cells lining blood vessels, in the organism's virulence strategy. We have found that R. oryzae damages endothelial cells in vitro and this process is dependent on iron. Additionally, we have cloned the R. oryzae high affinity iron permease (rFTRl) which scavenges iron from iron-depleted environments such as is found in vivo in the host. Finally we have developed clinically relevant models of infection in diabetic ketoacidotic mice. We hypothesize that iron uptake, and specifically rFTRl, is essential for R. oryzae to cause infection. To test this hypothesis, we propose to: 1) characterize the mechanism(s) by which iron regulates R. oryzae-induced endothelial cell injury; 2) construct an isogenic rftrl null mutant and its corresponding rFTRl complemented strain in R. oryzae by site directed mutagenesis; 3) compare the pathogenicity of the generated rftrl to that of the wild-type and rFTRl complemented strains in our in vitro and in vivo models of infection; and 4) elucidate the role of iron in regulating the innate host response to R. oryzae. Accomplishing these specific aims will define the role of the central elements affecting the establishment and progression of mucormycosis as it relates to iron uptake. Ultimately, a superior understanding of the pathogenesis of mucormycosis will enable development of novel therapies for this disease. Most immediately, completion of the proposed studies will lead to future investigation of the feasibility of treatments that block R. oryzae uptake of iron.